ANALYTICAL BIOCHEMISTRY 64, 98-101 (1975) Analysis of Dansyll-Amides in Mixtures by Mass Spectrometry, Using Metastable Defocusing F. ADDEO, ° A. MALORNI, 3 AND G. MARINO 4 Instituto di Chimica Organica e Biologica. Universitd di Napoli, Via Mezzocannone, 16 80134 Napoli, Italy Received July 17, 1974; accepted September 6, 1974 Analyses of mixtures of several dansyl-derivatives of biogenic amines were ob- tained by focusing the metastable ions related to the fragmentation process: molecular ion ---, dimethylaminonaphthalene ion. The method appears to be useful for the analysis of amines present in biological materials. In a recent paper (1) we have suggested the use of low energy electron bombardment for the analysis of dansyl-amides in mixtures by mass spectrometry. In studying the behavior of twenty dansyl-derivatives of natural amines under such conditions we have observed that the main fragmentation process, in several cases the only noticeable one, can be considered as follows: (CH3)oNC10H6SO~NR1R2]. + --~ (CH3)~NC10H7] + (m/e 17 1). We wish to report here a method of analysis of dansyl-amides in mix- ture based on this process. The method uses a metastable defocusing technique for ions formed by metastable decomposition in the first field- free region of a double-focusing mass spectrometer (2,3). This technique involves focusing on the collector a particular ion, in this case the fragment ion (role 171) and varying the accelerating voltage while the analyzer electrostatic voltage is kept constant. This has the ef- fect of focusing on the collector the precursor ions giving rise to this fragment during the travel from the source to the electrostatic analyzer. As we have observed that at low electron bombardment energy the main fragmentation process is that reported above, if a mixture of J Abbreviation used: Dansyl = dimethylaminonaphthalene-5-sulfonyl. -0 Permanent address: lstituto di lndustrie Agrarie dell'Universitfi di Napoli-Portici, Naples, Italy. Permanent address: Laboratorio Chimica e Fisica di Molecole di lnteresse Biologico del C.N.R.-Arco Felice, Naples, Italy. Author to whom correspondence should be addressed. 98 Copyright © 1975 by Academic Press, Inc. Printed in the United States. All rights of reproduction in any form reser,(ed.